Highly available particulate controlled release nitrogen fertilizer

Abstract

A method preparing controlled release nitrogen in particulate fertilizers which exhibit single growing season availabilities to plants of about 80 percent or higher. The method utilizes relatively low urea and ammonia to formaldehyde mol ratios of about 1.7 urea to 0.1 ammonia to 1 formaldehyde to assure high conversions to controlled release nitrogen with low free ureas, and carefully controlled elevated temperatures, acid dehydration condensation catalyst concentrations and short dehydration reaction times of about 2-4 minutes to provide effective conversion of hydroxymethyl nitrogen compounds by dehydration condensation reaction to controlled release methylene nitrogen compounds. Quick neutralization of the dehydration catalyst in a turbulent mixing reactor minimizes the formation of undesirable methylene nitrogen polymers which are hot water insoluble and unavailable to plants in a single growing season.

Description

1. Field of the InventionThis invention relates to controlled release nitrogen fertilizers and methods for their preparation. More particularly, the present invention is directed to a method of forming a new highly available slow release nitrogen fertilizer by condensing ammonia, urea, and formaldehyde under mildly basic conditions and elevated temperatures and then dehydrating the condensate without substantial polymerization to a controlled release solid fertilizer by means of a weak acid catalyst at elevated temperatures and short reaction times. The method provides granulation of homogeneous solids in a high intensity reactor either as a controlled release nitrogen, or complete N-P-K fertilizer. The new composition provided by this method provides higher nitrogen availabilities in high controlled release nitrogen concentrations than heretofore available.2. Description of Related ArtUreaformaldehyde condensation and polymer products are widely used as slow release nitrogen fertil...

AI Technical Summary

Benefits of technology

Another object of this invention is to provide a new composition containing plant nutrients bound together into physically homogeneous granules by nonpolymeric condensed methylene nitrogen compounds in highly efficient controlled release form.

I have now discovered that formaldehyde, urea, and ammonia may be reacted almost completely under base conditions to form water soluble liquid hydroxymethyl intermediates, such as methylolurea a nd methylolamine, and that these intermediates may be effectively converted to highly efficient controlled release particulate nitrogen fertilizers by a simple acid catalyzed condensation reaction and the reaction stopped before unavailable hot water insoluble nitrogen and free urea are formed in significant amounts. Further, the conditions which provide for driving the reaction to, and stopping it at, the efficient controlled release point, were discovered. It was found that the new method allowed the preparation and use of a new and improved controlled release nitrogen fertilizer.

An even better combination of high conversion of nitrogen to controlled release and high single season nitrogen efficiency or low hot water insolubility is obtained when the mol ratios of formaldehyde, urea, and ammonia are held in the narrow range between 1 to 1.70 to 0.03 and 1 to 1.80 to 0.10.

Particularly, when a narrow product particle size range is desired, appreciable amounts of extra, fine range product is available for recycle. It is advantageous to recycle this material as fertilizer solids for admixing during the dehydrating reaction of the preparation.

Problems solved by technology

Although the low HWIN is desirable, the high free urea is not because it increases phytotoxicity of the fertilizer significantly, and causes severe granulation difficulties by creating sticky operating conditions.

A high process recycle ratio and low process temperature must be used to granulate fertilizers containing high free urea contents because very small amounts of water cause urea containing solids to become sticky and difficult to granulate.

The amount of ammonia required and the anion required to neutralize it, undesirably increased the osmotic pressure, or osmolality, of the fertilizer.

Increasing osmolality has been shown to increase the phytotoxicity of a fertilizer.

When the CWIN is not soluble in hot water, it is known that the nitrogen is unavailable for plant utilization in the soil for a very long time, if ever.

This hot water insoluble nitrogen is undesirable, although many fertilizers found in commercial use have 60 percent or more of their CWIN in the form of hot water insoluble nitrogen (HWIN).

These cause the formation of undesirably large amounts of hot water insoluble nitrogen, which is unavailable to plants in a single growing season.

The polycondensation also results in the production of undesirable free urea from the intermediate methylolureas even when relatively low urea to formaldehyde mol ratios are used.

Unfortunately, these prior art improvements have been achieved by increasing other undesirable properties of the controlled release nitrogen fertilizers, such as increased free urea concentrations and burn potentials.